1. Field of the Invention
The present invention relates generally to a spindle motor and, more particularly, to a spindle motor having a plurality of sealing portions, having improved ability to seal fluid into a bearing portion, and enabling the storage of a larger amount of fluid.
2. Description of the Related Art
A spindle motor has a hydrodynamic bearing therein to generate dynamic pressure, and is installed in a hard disk drive or the like. Recently, as the spindle motor is applied to a portable product, such as an MP3 player or a mobile phone, attempts to miniaturize the spindle motor have been made. One example of a conventional spindle motor is shown in FIGS. 7 and 8.
As shown in FIGS. 7 and 8, a conventional spindle motor 400 includes a stationary part 401 and a rotary part 405 which is rotatably supported by the stationary part 401.
The stationary part 401 includes a base 410, a sleeve 420, a sealing cap 430, and an armature 440.
The base 410 functions to support respective parts of the stationary part 401, and is usually made of a non-magnetic material, such as aluminum alloy. Further, the base 410 includes a bottom portion 411, a sleeve supporting portion 412, and an outer wall portion 413. The bottom portion 411 has a disk shape, the sleeve supporting portion 412 has the shape of a cylinder which protrudes upwards from the center of the bottom portion 411, and the outer wall portion 413 extends upwards from the outer circumference of the bottom portion 411 to form a wall. Meanwhile, the sleeve 420 is supported by the sleeve supporting portion 412, and the base 410 is secured to a housing (not shown) of a device in which the motor 400 is installed, for example, a hard disk drive.
The sleeve 420 functions to rotatably support the rotary part 405, is made of a metallic material, and has a cylindrical shape. The lower end of the sleeve 420 is press-fitted into the sleeve supporting portion 412. The sleeve 420 is installed such that the central axis thereof corresponds to the central axis of a rotating shaft 470.
The sealing cap 430 has a disk shape, and serves to prevent fluid from leaking out of a bearing portion. The sealing cap 430 is secured to the sleeve 420 to close the lower end of the sleeve 420, thus preventing the leakage of the fluid from the bearing portion.
When external power is applied to the armature 440, the armature 440 forms an electric field. The armature 440 includes a core 441 which is secured to the outer wall of the sleeve supporting portion 412, and a coil 442 which is wound around the core 441.
Meanwhile, the rotary part 405 includes a rotor hub 460, the rotating shaft 470, and a magnet 480.
The rotor hub 460 serves to support respective parts of the rotary part 405, and is made of a magnetic material, such as steel. The rotor hub 460 has a disk portion 461, a cylindrical portion 462, and a disk mounting portion 463.
The rotating shaft 470 is integrally secured to the center of the disk portion 461. The disk portion 461 extends radially from the rotating shaft 470 in a disk shape. The cylindrical portion 462 extends from the outer circumference of the disk portion 461 to the free end of the rotating shaft 470 in a cylindrical shape. Further, the disk mounting portion 463 is the portion on which a recording medium, such as a disk, is mounted, and extends outwards from the outer circumference of the cylindrical portion 462 in a ring shape. Further, an inner wall 464 is mounted to the bottom of the disk portion 461 to be positioned inside the cylindrical portion 462.
The rotating shaft 470 is secured at one end thereof to the disk portion 461, or extends integrally from the disk portion 461, so that the other end of the rotating shaft 470 becomes the free end.
The magnet 480 is installed in the cylindrical portion 462 of the rotor hub 460 such that it is secured thereto and faces the armature 440.
In the motor 400 constructed as described above, a space SI between the outer circumference of the rotating shaft 470 and the inner circumference of the sleeve 420, a space S2 between the bottom surface of the rotating shaft 470 and the upper surface of the sealing cap 430, a space S3 between the bottom surface of the disk portion 461 of the rotor hub 460 and the upper surface of the sleeve 420, and a space S4 between the outer circumference of the sleeve 420 and the inner circumference of the inner wall 464 of the disk portion 461 communicate with each other, and are filled with fluid. Among the spaces, the spaces S1, S2, and S3 serve as the bearing portion when the rotary part 405 is rotated. Especially in the space S4 is formed a sealing surface, so that the space S4 serves as the sealing portion.
However, in the conventional motor 400 constructed as described above, the sealing portion, in which the sealing surface of the fluid is formed, is provided between the rotary part 405, specifically, the inner circumference of the inner wall 464 of the rotor hub 460, and the stationary part 401, specifically, the outer circumference of the sleeve 420. Thus, when the rotary part 405 is rotated, as shown in detail in FIG. 8, the fluid is driven to the inner wall 464 of the rotor hub 460 by centrifugal force, so that the fluid may undesirably leak out.